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From: Michal Hocko <mhocko@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"David S. Miller" <davem@davemloft.net>,
	Tony Luck <tony.luck@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	x86@kernel.org, linux-alpha@vger.kernel.org,
	linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
	linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH 02/11] locking, rwsem: drop explicit memory barriers
Date: Mon, 29 Feb 2016 13:58:16 +0100	[thread overview]
Message-ID: <1456750705-7141-3-git-send-email-mhocko@kernel.org> (raw)
In-Reply-To: <1456750705-7141-1-git-send-email-mhocko@kernel.org>

From: Michal Hocko <mhocko@suse.com>

sh and xtensa seem to be the only architectures which use explicit
memory barriers for rw_semaphore operations even though they are not
really needed because there is the full memory barrier is always implied
by atomic_{inc,dec,add,sub}_return resp. cmpxchg. Remove them.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 arch/sh/include/asm/rwsem.h     | 14 ++------------
 arch/xtensa/include/asm/rwsem.h | 14 ++------------
 2 files changed, 4 insertions(+), 24 deletions(-)

diff --git a/arch/sh/include/asm/rwsem.h b/arch/sh/include/asm/rwsem.h
index a5104bebd1eb..f6c951c7a875 100644
--- a/arch/sh/include/asm/rwsem.h
+++ b/arch/sh/include/asm/rwsem.h
@@ -24,9 +24,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_inc_return((atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_inc_return((atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -37,7 +35,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -53,9 +50,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -65,7 +60,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -76,7 +70,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_dec_return((atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -87,7 +80,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -108,7 +100,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -119,7 +110,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 
diff --git a/arch/xtensa/include/asm/rwsem.h b/arch/xtensa/include/asm/rwsem.h
index 249619e7e7f2..593483f6e1ff 100644
--- a/arch/xtensa/include/asm/rwsem.h
+++ b/arch/xtensa/include/asm/rwsem.h
@@ -29,9 +29,7 @@
  */
 static inline void __down_read(struct rw_semaphore *sem)
 {
-	if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
-		smp_wmb();
-	else
+	if (atomic_add_return(1,(atomic_t *)(&sem->count)) <= 0)
 		rwsem_down_read_failed(sem);
 }
 
@@ -42,7 +40,6 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 	while ((tmp = sem->count) >= 0) {
 		if (tmp == cmpxchg(&sem->count, tmp,
 				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
-			smp_wmb();
 			return 1;
 		}
 	}
@@ -58,9 +55,7 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 	tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
 				(atomic_t *)(&sem->count));
-	if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
-		smp_wmb();
-	else
+	if (tmp != RWSEM_ACTIVE_WRITE_BIAS)
 		rwsem_down_write_failed(sem);
 }
 
@@ -70,7 +65,6 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
 
 	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
 		      RWSEM_ACTIVE_WRITE_BIAS);
-	smp_wmb();
 	return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
@@ -81,7 +75,6 @@ static inline void __up_read(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
 	if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
 		rwsem_wake(sem);
@@ -92,7 +85,6 @@ static inline void __up_read(struct rw_semaphore *sem)
  */
 static inline void __up_write(struct rw_semaphore *sem)
 {
-	smp_wmb();
 	if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
 			      (atomic_t *)(&sem->count)) < 0)
 		rwsem_wake(sem);
@@ -113,7 +105,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
 {
 	int tmp;
 
-	smp_wmb();
 	tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
 	if (tmp < 0)
 		rwsem_downgrade_wake(sem);
@@ -124,7 +115,6 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
  */
 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
 {
-	smp_mb();
 	return atomic_add_return(delta, (atomic_t *)(&sem->count));
 }
 
-- 
2.7.0

  parent reply	other threads:[~2016-02-29 12:58 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-29 12:58 [PATCH 0/11] introduce down_write_killable for rw_semaphore Michal Hocko
2016-02-29 12:58 ` [PATCH 01/11] locking, rwsem: get rid of __down_write_nested Michal Hocko
2016-02-29 12:58 ` Michal Hocko [this message]
2016-02-29 12:58 ` [PATCH 03/11] locking, rwsem: introduce basis for down_write_killable Michal Hocko
2016-03-30 13:25   ` Peter Zijlstra
2016-03-31  8:33     ` Michal Hocko
2016-03-31  8:44       ` Peter Zijlstra
2016-03-31  8:55   ` [PATCH] " Michal Hocko
2016-02-29 12:58 ` [PATCH 04/11] alpha, rwsem: provide __down_write_killable Michal Hocko
2016-02-29 12:58 ` [PATCH 05/11] ia64, " Michal Hocko
2016-02-29 12:58 ` [PATCH 06/11] s390, " Michal Hocko
2016-02-29 12:58 ` [PATCH 07/11] sh, " Michal Hocko
2016-02-29 12:58 ` [PATCH 08/11] sparc, " Michal Hocko
2016-02-29 12:58 ` [PATCH 09/11] xtensa, " Michal Hocko
2016-02-29 12:58 ` [PATCH 10/11] x86, " Michal Hocko
2016-02-29 12:58 ` [PATCH 11/11] locking, rwsem: provide down_write_killable Michal Hocko
2016-03-30 13:32 ` [PATCH 0/11] introduce down_write_killable for rw_semaphore Peter Zijlstra
2016-03-31  8:59   ` Michal Hocko
2016-03-31  9:20     ` Ingo Molnar
2016-03-31 10:58       ` Michal Hocko
2016-03-31 17:03       ` Andrew Morton
2016-04-01  6:33         ` Ingo Molnar
2016-04-01  9:21           ` Michal Hocko
2016-04-01  9:50             ` Ingo Molnar
2016-04-01 10:52               ` Michal Hocko
2016-04-01  7:26         ` Michal Hocko
2016-04-01  9:11           ` Andrew Morton
2016-04-01 11:04 [PATCH 0/11] introduce down_write_killable for rw_semaphore v2 Michal Hocko
2016-04-01 11:04 ` [PATCH 02/11] locking, rwsem: drop explicit memory barriers Michal Hocko
2016-04-02  1:17   ` Davidlohr Bueso
2016-04-04  9:03     ` Michal Hocko
2016-04-07 15:12 [PATCH 0/11] introduce down_write_killable for rw_semaphore v3 Michal Hocko
2016-04-07 15:12 ` [PATCH 02/11] locking, rwsem: drop explicit memory barriers Michal Hocko

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